This invention relates to the fabrication of bioprosthetic heart valve replacements. Valve replacements are required for patients having a heart valve which is diseased or otherwise incompetent. Commonly, heart valve bioprostheses are made from a combination of animal tissue and mechanical elements. These bioprostheses have an advantage over purely mechanical valves in that they do not require the use of anticoagulant therapy that plagues purely mechanical valves.
U.S. Pat. No. 5,163,955 (the '955 patent) discloses such a bioprosthetic valve, in which an inner stent, on which the tissue used to construct the valve is wrapped, is inserted into a spreadable outer stent containing a self-adjusting tensioning spring around the circumference of its base. The inner stent posts are fitted with a plurality of outwardly-projecting pegs which register with holes cut in the tissue, and the inner stent assembly is covered with cloth. The spread outer stent clamps the stents together at its base and at a plurality of posts projecting from the bases of both the inner and outer stents. This clamping thus secures the tissue while compensating for irregularities and supplying a clamping force which is evenly distributed over the entire circumference of the tissue.
The outer stent disclosed in the '955 patent has an annular base constructed with a groove around its circumference, into which a self-adjusting tensioning means such as a garter spring is fitted. The garter spring provides a clamping force when the inner stent is inserted into the outer stent. Additionally, the posts on the outer stent are configured with windows surrounded by struts, which give shape to the post. The window is shaped to conform to the shape of the inner stent posts while leaving a small gap between the inner stent posts and the struts when the inner stent is inserted into the outer stent. Such an arrangement facilitates the insertion of the inner stent into the outer stent and provides for a uniform application of the clamping force to the tissue.
At the bottom of each of the windows in the outer stent posts are slots which segment the base into a plurality of arcuate portions. The slots enable the outer stent to be spread open so that it can easily be fitted over the inner stent without damaging the tissue during the valve assembly process.
An elastomeric sewing ring is bonded to the base of the outer stent assembly to facilitate the sewing of the assembled heart valve into the patient. The entire assembly is covered with a fabric cover, typically made out of DACRON, which is bonded to the bottom of the outer stent base.